A warning device that produces a warning about an object is proposed in JP-A-11-139229. If an object that is not recognized by a driver of a vehicle exists, the warning device determines a warning level based on a distance and a bearing between the object and the vehicle. Then, the warning device produces the determined level of warning.
The warning device determines whether an object is located in a vision of the driver to determine whether the driver has recognized the object. However, the driver may not have recognized the object if the driver does not carefully look at the object. Thus, the warning device could erroneously determine the recognition of the object by the driver. Namely, it cannot properly determine whether the object is an obstacle to the vehicle.